This project will examine morphological and functional aspects of age-related alterations in the magnocellular vasopressin neurosecretory system. The rat brain will be examined in an attempt to determine its applicability to the study of human aging. A multifaceted, integrated approach will employ techniques of peptide immunocytochemistry, at the light and electron microscopic level, transmitter histochemistry, computer-assisted dendrite tracking in golgi stained preparations radioimmunoassay of vasopressin. Physiological parameters of vasopressin secretion in humans as a function of age will be measured and correlated with comparable studies in the rat model.